|  | 8.5 | Server Administration
| 8.5.2 | Client-server
The other type of network is a client-server network. Network operating systems are the heart of the client-server network. These systems control the resources and management of the local area network. The advantages of client-server networks are, they provide a centralized point of user, security, and resource management. Also dedicated servers can be used to more effectively provide specific resources to clients. They also provide access to all allowed resources with one network ID and password. The disadvantages are that there is now a single point of failure in the network. If the server "goes down", all server resources are unavailable to the clients. In fact, the clients may not even operate without the server. Network operation and maintenance now require specially trained personnel to maintain the network. This along with special network software and hardware add greatly to the cost of operation. Even with the disadvantages, a client-server network is really the only choice for businesses with more than ten users. Examples of client-server operating systems are Unix, Novell NetWare, and Windows NT. The Unix operating system comes in many variations, as implemented by different companies. Companies that provide Unix include Sun Microsystems, IBM, Hewlett-Packard and Santa Cruz Operation (SCO). There are also free versions of Unix called FreeBSD and Linux, the latter of which has great popularity at the present time. Unix is a multi-user operating system that supports multiprocessing, multitasking, and multithreaded applications. The operating system is Kernel based, which isolates the hardware layer of the computer from improperly operating applications and primarily uses the NFS (Network File System - Sun Microsystems's implementation) file system. The NFS file system provides for both file and directory security access on the server. Unix also provides for centralized user and resource control through the operating system. Because of the multiple versions of Unix that are in production, it is difficult to contrast all of the variations and releases of this software. The description above gives the common features available in all Unix "flavors". Clients that work best with Unix are usually specific to the developer of the operating system. In discussing NetWare and Windows NT, we must also talk about the different versions that have evolved over the years. First we will cover Novell NetWare. The versions of NetWare that will be covered are Ver 3.12, Ver. 4.11, and Ver. 5.0. These versions primarily differ in their handling of Directory services. NetWare Ver. 3.12 uses an object called the Bindery to manage multiple users and resources. The drawback is that bindery services create a server-centric network. A server-centric network is focused on the individual server as the point of control. This creates a problem with a multiple server network. Each server still must have an individual ID for each user, even though the passwords could be synchronized so that changing one would change the password on all servers, this defeats the purpose of centralized management. To be fair this is a time issue, Ver 3.12 was in existence before the great explosion of multi-server networks. This is one of the major improvements in NetWare Ver 4.11. NetWare Ver 4.11 and Ver 5.0 use an object called the NDS (Novell Directory Services) to manage users and resources. The advantage over Ver 3.12 is that NDS creates a network-centric network. A network-centric network is focused on the entire network as the point of control. This focus consolidates management to a single point and servers are treated just as objects within the context of the network. This allows a single ID and password to authorize users for all resources across the network and provides for easier network organization and management. All versions of NetWare use a combination of two file services. The first being FAT (file allocation table), which is the file system used for DOS. The second, being DET (Directory Entry Table) which is a proprietary Novell file system which provides for both file and directory security on the server. Clients that work well with NetWare are numerous; they include all versions of Windows, DOS, Macintosh, and OS-2. NetWare's strong points are user and file resource management. Windows NT is the last operating system to be discussed. There are two versions of Windows NT to cover. Windows NT ver 4.0 server and workstation were developed with the Windows 95 user interface. This provides a consistent "look and feel" interface across all Windows products. Windows NT handles user and resource management through the use of Domains. A domain is a logical grouping of users and resources under the control of one server called the PDC (Primary Domain Controller). Domains also support the use of secondary servers called BDC's (Backup Domain Controllers). BDC's balance the workload of the PDC and provide for redundancy of user and resource objects. A third type of server is allowable in a Domain; it is called a stand-alone server. This server is primarily setup to support one particular application and dedicate its resources to that application. Another variation of a domain is called a multi-domain model. In this model separate domains are connected by trusting-trusted relationships, this allows users to cross Domain boundaries to use resources. The Windows 2000 Server management structure will change from Domains to an Active Directory Structure. Active directory is based on a network-centric model, like NDS, rather that a Domain centered model. Windows NT is just like Unix, a multi-user operating system that supports multiprocessing, multitasking, and multithreaded applications. The operating system is, just like Unix, Kernel based, which isolates the hardware layer of the computer from improperly operating applications and uses the both the FAT16 file system and NT's own proprietary system, NTFS (New Technology File System). With FAT16, Windows NT provides just directory (or also known as folder) level security; no individual file security is provided. NTFS provides both file and directory level security and permissions. The reason that Windows NT supports both of these operating systems is that it has the ability to coexist with another operating system on the same machine. This doesn't mean that both systems can run at the same time, but the computer can run Windows NT or the other operating system. For the other operating system to have file access the file system must be FAT16. Just as a point of interest, Windows 95 and 98 support FAT32, Windows NT doesn't. So FAT16 would be the choice for running Windows NT and 95 on the same computer. Windows NT works best with its own client, Windows NT Workstation, but also works well with Windows for Workgroups, Windows 95 and 98, and Macintosh clients. No matter which Network Operating System is used, the main function of the NOS is to control the network. This is accomplished by establishing network user; Rights, Login accounts (user Ids), Passwords, and Groups, along with System Profiles and Policies. These terms will be identified more completely in the following paragraphs.
| Web Links
| Network Operating System Tutorial
| Netware NDS Tutorial I
| Netware NDS Tutorial II
| Unix Tutorial